You cannot show a dialog on non-activity context. But, You can design a transparent activity to make it look like dialog and call it from Device Admin as following:
Intent intent = new Intent(context, YourActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(intent);
context declared in the code above is an attribute for any action method inside DeviceAdminReceiver
class. For better understanding check following:
@Override
public CharSequence onDisableRequested(Context context, Intent intent) {
Intent intentcl = new Intent(context, OperationActivity.class);
intentcl.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(intentcl);
return super.onDisableRequested(context, intent);
}